Blood clots in cerebral arteries and other vessels of the brain can cause strokes and other neurological problems. It is therefore desirable that these blood clots be broken up and removed. One technique which has been utilized to accomplish this objective in the past is laser ablation. However, because of the tortuous nature of the brain vessels and the vessels leading thereto, moving a catheter into a position to deliver light energy to a clot requires that the catheter, or at least the distal portion thereof, be very flexible, and normally requires that the catheter be advanced over a guidewire to a desired location. However, a light delivery catheter also normally requires a light guide passing through the catheter. But, a catheter having two lumens passing therethrough, one for a guidewire and one for a light guide, would be too stiff, particularly at the distal end thereof, to traverse the tortuous path to the brain; therefore catheters used for ablation of brain clots have heretofore utilized a single lumen, with the guidewire being removed when the catheter is positioned adjacent a clot and a light guide then inserted through the catheter to a position adjacent the clot.
However, in order to avoid damaging parts of the vessel other than the clot, or even puncturing the vessel, relatively low energy is used for such procedures, so that the first delivery of light energy to the clot normally does not result in ablation thereof. In order for the procedure to be most effective, it is desirable that the catheter be repositioned adjacent to the new leading edge of the clot before light energy is again provided. However, it is also preferable that the guidewire be utilized for such repositioning. Therefore, with current equipment, the doctor performing the procedure has had three choices, namely (a) attempt to reposition the catheter without the use of a guidewire; (b) not reposition the catheter and continue ablation from the catheter's original position; or (c) remove the light guide through what may be as much as 150 centimeters (approximately 5 feet) of catheter, reinsert a guidewire to reposition the catheter, and then remove the guidewire and reinsert the light guide. The first procedure is difficult to perform, the second results in reduced energy being transmitted to the clot for subsequent applications of light energy and, because of the tortuous nature of the vessel, may result in light being directed at a portion of the vessel other than the clot, resulting in reduced clot ablation. The third procedure is tedious and time-consuming. Therefore, existing light delivery catheters for laser thrombosis or ablation of blood clots impose limitations on the doctors performing such procedures and result in less than optimum procedures being utilized. The same problems arise where the laser is only used to cavitate the clot and a clot-busting drug such as tPA is used in conjunction with ablation/cavitation to assist in breaking up the clot. This procedure also requires in most instances several iterations of light energy and drug application before the blood clot is fully broken up.
Another potential problem in using a light delivery catheter to remove a blood clot in the brain is that vessel walls in the brain are relatively thin and subject to perforation, particularly by a catheter being pressed there against. This risk is reduced by having a very flexible guidewire being used to lead the catheter through the vessel and by not having an unguided catheter moving forward through the vessel.
Still another potential problem is that, since the blockage at a clot prevents any emboli created during the lysing or ablation process from being washed downstream, such emboli therefore must travel retrograde or upstream to areas of the brain which are unaffected by the clot. These emboli or particles traveling through vessels which may already be narrowed by the presence of the catheter therein can, in a worse case scenario, result in a stoke in such unaffected areas of the brain. It would therefore be preferable if such emboli could be washed or flushed downstream through vessels in area of the brain already affected by the stoke and through vessels not partially blocked by a catheter so as to both reduce the likelihood of a further small stroke and to minimize any new damage caused thereby.
Finally, all of the current procedures for the ablation of blood clots in the brain are relatively time consuming. Since the longer the procedure, the harder it is on both the physician and patient, and the more expensive the procedure becomes, it is desirable that any procedure utilized be as efficient as possible so as to minimize the time required for its performance.
Similar problems may exist when using a light-delivery catheter to remove clots from blood vessels in parts of the body other than the brain. A need therefore exists for an improved light delivery catheter which permits the catheter to be sufficiently flexible, at least in the distal portion thereof, to advance through tortuous brain or other vessels with minimum risk of damage thereto while still permitting rapid exchange between guidewire and light guide so as to facilitate rapid and accurate repositioning of the catheter adjacent the current leading edge of the clot between each delivery of light energy. It is also desirable that the catheter used operate in a fluid flow mode, facilitating the delivery of light energy to the clot and that the procedure used facilitate washing of emboli creating by the ablation process downstream so as to minimize risk of secondary stroke, particularly in unaffected areas of the brain.